Prostanoic acid derivatives and preparation thereof

ABSTRACT

THERE ARE DISCLOSED HEARIN 9,15-DIOXOPROSTANOIC ACID, LOWER ALKYL ESTERS THEREOF, AND HOMOLOGS THEREOF, A PROCESS TO PREPARE THOSE COMPOUNDS. AS WELL AS A PROCESS FOR PREPARING 9,15-DIHYDROXYPROSTANOIC ACID, LOWER ALKYL ESTERS THEREOF, AND HOMOLOGS THEREOF. THE COMPOUNDS POSSESS HYPOTENSIVE AND ANTIHYPERTENSIVE ACTIVITIES, AND METHODS FOR THEIR USE ARE ALSO DISCLOSED.

ABSTRACT OF THE DISCLOSURE There are disclosed herein 9,15-dioxoprostanoic acid, lower alkyl esters thereof, and homologs thereof, a process to prepare those compounds, as well as a process for preparing 9,15-dihydroxyprostanoic acid, lower alkyl esters thereof, and homologs thereof. The compounds possess hypotensive and antihypertensive activities, and methods for their use are also disclosed.

This application is a division of our prior, copending application, Ser. No. 769,750, filed Oct. 22, 1968, now

abandoned.

BACKGROUND OF THE INVENTION This invention relates to 9,15-dioxoprostanoic acid, to

lower alkyl esters thereof, and to homologs thereof, as well as to a process for preparing said compounds and to a process for preparing 9,15-dihydroxyprostanoic acid, lower alkyl esters thereof, and homologs thereof. The compounds of this invention are structurally related to the natural prostaglandins which are more fully described in their biological activities and chemical structures in the Proceedings of the Second Nobel Symposium, Stockholm, June 1966, and in the review paper by U. Axen published in Annual Reports in Medicinal Chemistry, Academic Press, p. 290, New York and London, 1968. The prostaglandins occur in nature only in very small quantities, and the processes for their extraction and purification from" natural sources are laborious and inefiicient. It is an object of this invention to provide compounds structurally related to the naturally occurring prostaglandins by synthetic means.

SUMMARY OF THE INVENTION .The compounds of this invention may be represented by the 'Formulal R OOOR' R represents hydrogen or a lower alkyl group of from-l to .3"carbon atoms, and n represents an integer of from United States Patent Ho 6. The process of this invention is exemplified inthe 3,808,258 Patented Apr. 30, 1974 p CC o (cnnoooiv v cm pent) VIIb DETAILED DESCRIPTION OF THE INVENTION Our preferred starting material for thepreparationof 9,15 dioxoprostanoic acid is 2 (6-carbomethoxyhexyl)- cyclopent-2'en-1-one. The preparation of the. corresponding 2-(6-carboxyhexyl)cyclOpent-Z-en-l-one is described in 'our U.S. patent application Ser. No. 485,935, filed Sept. 8, 1965. In-accordan'ce with the methoddescribed therein, thelatter compound is obtained by condensing the known compound ethyl 7 bromo-l-heptanoate with the equally known "potassium salt of ethyl cyclopentanone'carboxylate, by refluxing a mixture of the two compounds in an.

pentan-1-one-2-carboxylate; treating the latter compound with elementary bromine in chloroform solution to obtain ethyl 2 (6-carbethoxyhexyl)-5-bromocyclopentan-1-0ne- 2-carboxylate; treating the latter compound with a mineral acid, preferably 20% sulfuric acid, to obtain 2-(6- carboxyhexyl)-cyclopent-2-en-1-one; and treating the latter compound with methanol and p-toluenesulfuric acid to obtain 2-(6-carbomethoxyhexyl)-cyclopent-2-en-1-one (II) R='CH For the purposes of this invention other lower alkyl esters of the above acids, such as the ethyl or propyl esters, may also be used.

In a preferred procedure for the preparation of 9,15- dioxoprostanoic acid and of its derivatives, the last-named compound of Formula II is reacted with a vinyl ketone of the Formula III containing from 6 to 11 carbon atoms.

If it is desired to prepare 9,15-di0xoprostanoic acid L (I,R=O(ketonic oxygen), rt=4), the starting material is 1-chloro-3-oxo-oct-l-ene, prepared according to the general procedure described in Organic Syntheses, vol. 32, p. 27 (1952). The reaction is preferably carried out in the absence of a solvent, by irradiation with a 500W mercury vapor lamp with Pyrex filter and water cooling at -40" C. for 24 to 48 hours. Evaporation under reduced pressure followed by purification, for example by chromatography, yields 7 hexanoyl 6 chloro-2-oxobicyclo- [3,2,0]-heptane-1-heptanoic acid methyl ester (IV, H

R-'=CH n=4). The latter compound, treatment with ap proximately 20 parts of zinc and acetic acid at temperatures between 60 C. and the boiling point of the mixture of several hours, preferably overnight yields a mixture of 7-hexanoyl-2-oxobicyclo-[3,2,0]-heptane-1-heptanoic acid methyl ester and 9,15-dioxoprostanoic acid methyl ester (VI, R=CH rn=4) which is separated, preferably by chromatography. Using approximately 30 parts of zinc per part of Compound IV it is possible to obtain predominantly the compound of Formula VI. However, it

is also possible to convert the compound of Formula V to that of Formula VI by an additional treatment with zinc and acetic acid.

The 9,15-dioxoprostanoic acid methyl ester (VI, R=CH )thus obtained may be subjected to alkaline hydrolysis to yield the corresponding prostanoic acid (VI, R=H, m=4).

Alternatively, 9,15-dioxoprostanoic acid methyl ester (VI, R=CH n=4) is reduced with sodium borohydride to give a mixture of stereoisomeric alcohols, 9 9,15-dihydroxyprostanoic acid methyl ester (VIIIa, R=CH n=4-) and 9a,15-dihydroxyprostanoic acid methyl ester (VIIb, R=CH, n==4). Alkaline hydrolysis of the last-named compounds yields the corresponding 913,15gand 911,155- dihydrox-yprostanoic acids of Formulae VIIa and VIIb, respectively (R=H, n=4).

In the same manner as described above, but using as the chlorovinyl ketones chlorovinyl methyl, ethyl, propyl, butyl, or hexyl ketones, and proceeding as above, there are obtained the compounds of Formula IV (R-=lower alkyl, and m=1,2,3,5 or 6), viz, 7-acetyl-, 7-propionyl-, 7-butanoyl-, 7-pentanoyl+, 7-heptanoyl-, and 7-octanoyl- 6 chloro 2 oxobicyclo [3,2,0] heptane lheptanoic acid lower alkyl esters, respectively. The latter compounds are converted by treatment with zinc and acetic acid in the same manner as described above to mixtures of the corresponding compounds of Formula V (R=lower alkyl, n=1,2,3,5, or 6) viz, 7-acetyl-, 7- propionyl-, 7-butanoyl-, 7-pentanoyl-, 7-heptanoyl-, or 7- octanoyl 2 oxobicyclo [3,2,0]-heptane-1-heptanoic acid lower alkyl esters with the respectively corresponding compounds of Formula VI (R=lower alkyl, m=l,2, 3,5, or 6) viz, the trans-lower alkyl esters of 2-(6-carboxyhexyl)-3-oxobutyl-, 3-oxopentyl-, 3-oxohexyl-, 3-oxoheptyl-, or 3-oxonoyl-, or 3-oxodecyl-cyclopentan-l-one. The last-named compounds may be reduced in the same manner as described above to yield the corresponding compounds of Formulae VIIa and VIIb (R=lower alkyl, n=1,2,3,5, or 6), viz, trans 2 (6-carboxyhexyl)-3-(3- 47 hydroxybutyl)-, (3.5 hydroxypentyl)-, (3.5-hydroxy- 'hexyl)-, (3E hydroxyheptyl-, (3g hydroxynonyl)- or (35 hydroxydecyl)-cyclopentan-1a-and 15-01, respectively.

The compounds prepared by the process of this invention have been found to possess interesting pharmacological properties. More particularly, these compounds, in standard pharmacological tests, especially in a modification of the tests for determining hypotensive activities described in Screening Methods in Pharmacology, Academic Press, New York and London 1965, page 146, using the cat in urethane-chloralose anaesthesia as the test animal and measuring mean arterial blood pressure before and after intravenous administration of the compounds, have exhibited utility as hypotensive agents.

Moreover, the compounds of this invention, when tested in the renal hypertensive rat prepared by themethod of A. Grollman described in Proc. Soc. Exp. Biol. Med., vol. 7, p. 102 (1954), and measuring blood pressure by the method described by H. Kersten in J. Lab. Clin. Med., vol. 32, p. 1090 (1947), have exhibited utility as antihypertensive agents.

When the compounds of this invention are employed as hypotensive agents in warm-blooded animals, for example, in cats or rats, alone or in combination with pharmacologically acceptable carriers, their proportions are determined by their solubilities, by the chosen route of administration, and by standard biological practice. For example, the compounds of this invention are preferably administered parenterally in the form of sterile solutions thereof which may also contain other solutes, for example, sufiicient sodium chloride or glucose to make the solution isotonic.

The dosages of the present hypotensive and antihypertensive agents will vary with the forms of administration and the particular compounds chosen. Furthermore, they will vary with the particular hosts under treatment. Generally, treatments are initiated with small dosages substantially less than the optimum doses of the compounds. Thereafter, the dosages are increased by small increments until the optimum elfects under the circumstances are reached. In general, the compounds of this in- EXAMPLE 1 7-hexanol-6-chloro-2-oxobicyclo- [3,2,0] -heptane-1- heptanoic acid methyl ester (IV) A solution of 2-(6-carbomethoxyhexyl) -cyclopent-2-en l-one (4.52 g.) in l-chloro-3-oxooct-1-ene is irradiated with 500 watt mercury arc (with Pyrex filter) over a period of 28 hours, under nitrogen atmosphereThe reaction is stopped and the mixture is fractionally distilled to remove unchanged chlorovinyl ketone (B.P., 80-83" C./ 12 mm.), and cyclopentenone (bath temperature C./ 1.5 mm.) The residue is chromatographed on a column of silica gel g.) in benzene. Elution with 2% etherbenzene yields a product (1.6 g.). A rechromatography on silica gel yields the title compound as an oil which is homogenous by thin-layer and gas-liquid chromatography and is characterized by analysis, by N.M.R. spectrography 64.50 (1H, quartet, on carbon bearing chlorine) 63.17 (1H, or to ketone, on cyclobutane) 63.65 (3H, methoxyl) 60.88 (3H, terminal methyl) and by mass spectrography M36: 348; M(36+31): 317, M-(36+99:) 249 m./c.

EXAMPLE 2 7-hexanoyl-2-oxobicyclo [3,2,0] -heptane-1-heptanoic acid methyl ester (V) A solution of 7-hexanoyl-6-chloro-2-oxobicyclo-[3,2,0]- l-heptanoic acid (0.454 g.) in glacial acetic acid (30 ml.) is refluxed with stirring overnight, in presence of zinc (2.76 g.). The mixture is filtered and the solvent removed. The residue is taken up in ether, washed with water, dried, and the solvent is removed, to yield an oily residue, a mixture of Compounds HI and IIIa, which is separated by chromatography as silica gel. The title compound is eluted with 5 percent ether/benzene and is obtained in the first fractions with $5,9 1700, 1725 emf it is further characterized by mass spectrography (M: 350 m./c.; M-31: 319 m./c.; M-99: 251 m./c.; M-71: 271 m./c.; and by N.M.R. 63.65 (3H, methoxyl); 63.05 (1H, to carbonyl on cyclobutane) 60.88 (3H, terminal methyl).

EXAMPLE 3 9,15-dioxaprostanoic acid methyl ester (VI) To a solution of 7 hexanoyl 6 chloro-2-oxobicyclo- [3,2,0]-heptane-l-heptanoic acid methyl ester (0.5 g.) in acetic acid (30 ml.) is added zinc dust (7.5 g.) and the mixture is stirred overnight, at reflux temperature, cooled, and filtered. The residue is washed with ether, and the solvent is completely removed. The residue is taken up in ether, washed with water, dried, and the solvent is removed. The residue is chromatographed on silica gel (23.6 g.) and the later eluates with ether/benzene yield the title compound as a homogenous product 'yfff 1726, 1708 cm.-

Alternatively, the title compound may also be prepared as follows.

To a solution of 7-hexanoyl-2-oxomethyl ester (0.35 g.), obtained as described in Example 2, in acetic acid (25 ml.) zinc dust g.) is added and the mixture is heated in an oil bath at 115 overnight. The reaction mixture is cooled and filtered. The solvent is removed and the residue taken up in ether, washed with water, dried and the solvent is removed to yield the title compound as an oil, identical with the compound as described above,

EXAMPLE 4 9a and 913, -E-dihydroxyprostanoic acid methyl ester (VIIa, VIIb) To a solution of 9,15-dioxoprostanoic acid methyl ester (0.420 g.) in methanol (6 ml.) is added sodium borohydride (0.157 g.). The reaction mixture is stirred for 30 minutes and diluted with ether. The organic extract is washed with 2-3 ml. of 3% hydrochloric acid, followed by water and saline, dried, and the solvent is removed.

The residual oil is chromatographed on silica gel 6 (Merck, 0.05 mm.0.2 mm., 25 g.) in 40% ethyl acetatebenzene to yield the title compounds 9,8,155-dihydroxyprostanoic acid methyl ester and 9m,15-dihydroxyprostanoic acid methyl ester characterized by and by N.M.R. (CDC1 spectrography, where 95,15-dihydroxyprostanoic acid methyl ester has 63.94 (1H, ring carbinolic) 63.71-352 (4H, 3 of methoxyl singlet, and 1 carbinolic) and 9a,l5g-dihydroxyprostanoic acid methyl ester has 64.29 (1H ring carbinolic) 63.72-352 (4H, 3 of methoxyl, 1 carbinolic.)

EXAMPLE 5 9,15-dioxoprostanoic acid (VI, R=H) To a solution of 9,15-dioxoprostanoic acid methyl ester (0.3 g.) in methanol (2 ml.) is added sodium hydroxide solution (0.5 ml., 10%) and the mixture is stirred overnight, under nitrogen atmosphere. The reaction mixture is diluted with ether, and washed with water. The aqueous layer is acidified and reextracted with ether, the ether layer is dried and the solvent is removed to yield 9,15-dioxoprostanoic acid,

EXAMPLE 6 9a,l5g-Dihydroxyprostanoic acid (VI'Ia and VIIb) To a solution of 9a,158-dihydroxyprostanoic acid methyl ester (0.085 g.) in methanol (2 ml.) there is added 0.2 ml. of sodium hydroxide solution (10 percent) and the mixture is stirred overnight at room temperature. The reaction mixture is diluted with ether, to remove non-acidic material. The aqueous layer is acidified with 10 percent hydrochloric acid and extracted with ether. The ether layer is dried and the solvent is removed, to yield 9a,l56- dihydroxyprostanoic acid (VIIa, R=H), crystallized from acetone-hexane to M.P. 97-8 C.,

12123375, 1700 emf In a similar manner as described above 93,156-dihydroxyprostanoic acid methyl ester is hydrolyzed to the corresponding 9,3,15-dihydroxyprostanoic acid which is obtained as an oil with 'y,,,.,, 3378, 1700 cmf We claim:

1. 7-hexanoyl-6 chloro 2 oxo[cis]bicyclo-[3,2,0] heptane-l-heptanoic acid methyl ester.

References Cited UNITED STATES PATENTS 3,671,570 6/1972 Bagh et a1 260-468 LCRRAINE A. WEINBERGER, Primary Examiner R. GERSTL, Assistant Examiner US. Cl. X.'R.

260468 D, 514 D, 514 G 

